Tao Ran, Rice Kirk D, Djakeu Anicet S, Mrozek Randy A, Cole Shawn T, Freeney Reygan M, Forster Aaron M
Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
Department of Chemical Engineering, Texas Tech University, Lubbock, TX 79409, USA.
Polymers (Basel). 2019 Mar 8;11(3):447. doi: 10.3390/polym11030447.
Roma Plastilina No. 1 (RP1), an artist modeling clay that has been used as a ballistic clay, is essential for evaluation and certification in standards-based ballistic resistance testing of body armor. It serves as a ballistic witness material (BWM) behind the armor, where the magnitude of the plastic deformation in the clay after a ballistic impact is the figure of merit (known as "backface signature"). RP1 is known to exhibit complex thermomechanical behavior that requires temperature conditioning and frequent performance-based evaluations to verify that its deformation response satisfies requirements. A less complex BWM formulation that allows for room-temperature storage and use as well as a more consistent thermomechanical behavior than RP1 is desired, but a validation based only on ballistic performance would be extensive and expensive to accommodate the different ballistic threats. A framework of lab-scale metrologies for measuring the effects of strain, strain rate, and temperature dependence on mechanical properties are needed to guide BWM development. The current work deals with rheological characterization of a candidate BWM, i.e., silicone composite backing material (SCBM), to understand the fundamental structure⁻property relationships in comparison to those of RP1. Small-amplitude oscillatory shear frequency sweep experiments were performed at temperatures that ranged from 20 °C to 50 °C to map elastic and damping contributions in the linear elastic regime. Large amplitude oscillatory shear (LAOS) experiments were conducted in the non-linear region and the material response was analyzed in the form of Lissajous curve representations with the values of perfect plastic dissipation ratio reported to identify the degree of plasticity. The results show that the SCBM exhibits dynamic properties that are similar in magnitude to those of temperature-conditioned RP1, but with minimal temperature sensitivity and weaker frequency dependence than RP1. Both SCBM and RP1 are identified as elastoviscoplastic materials, which is particularly important for accurate determination of backface signature in body armor evaluation. The mechanical properties of SCBM show some degree of aging and work history effects. The results from this work demonstrate that the rheological properties of SCBM, at small and large strains, are similar to RP1 with substantial improvements in BWM performance requirements in terms of temperature sensitivity and thixotropy.
罗马塑料黏土1号（RP1）是一种曾被用作弹道黏土的艺术家造型黏土，在基于标准的防弹衣弹道抗性测试的评估和认证中至关重要。它作为防弹衣后方的弹道见证材料（BWM），弹道冲击后黏土中的塑性变形量即为品质因数（称为“背面特征”）。已知RP1表现出复杂的热机械行为，这需要进行温度调节和频繁的基于性能的评估，以验证其变形响应是否满足要求。人们期望有一种不太复杂的BWM配方，允许在室温下储存和使用，并且具有比RP1更一致的热机械行为，但是仅基于弹道性能的验证对于适应不同的弹道威胁来说将是广泛且昂贵的。需要一个实验室规模的计量框架来测量应变、应变速率和温度依赖性对力学性能的影响，以指导BWM的开发。当前的工作涉及一种候选BWM即硅酮复合背衬材料（SCBM）的流变学表征，以便与RP1相比了解基本的结构-性能关系。在20℃至50℃的温度范围内进行了小振幅振荡剪切频率扫描实验，以描绘线性弹性区域中的弹性和阻尼贡献。在非线性区域进行了大振幅振荡剪切（LAOS）实验，并以李萨如图形表示的形式分析了材料响应，报告了完美塑性耗散比的值以确定塑性程度。结果表明，SCBM表现出的动态性能在量级上与温度调节后的RP1相似，但温度敏感性最小，频率依赖性比RP1弱。SCBM和RP1都被确定为弹黏塑性材料，这对于在防弹衣评估中准确确定背面特征尤为重要。SCBM的力学性能表现出一定程度的老化和工作历史效应。这项工作的结果表明，SCBM在小应变和大应变下的流变性能与RP1相似，在温度敏感性和触变性方面对BWM性能要求有显著改善。
